1. Field of the Invention
The present invention relates to a system that slices silicon ingots used as the material for semiconductors, or the like. The present invention also relates to a method and apparatus for adhering ingots to support members, which are used to mount ingots on slicing machines, and an ingot slicing method.
2. Description of the Related Art
Semiconductor wafers are generally formed by slicing ingots, which are constituted by silicon monocrystals, into a predetermined thickness using a wire saw or the like. An example of one method to slice the ingots will now be described. As shown in FIG. 3, an ingot 13 is lifted out of a crucible (not shown) and machined cylindrically. An intermediate plate 20, which is made of carbon or the like, is adhered to the cylindrical surface of the ingot 13. A support plate 21 (FIG. 6) is adhered to the upper surface of the intermediate plate 20 with a glass insulating plate 21a arranged therebetween. As shown in FIG. 13, the ingot 13 is mounted on a wire saw 326 by way of the support plate 21.
The wire saw 326 includes a plurality of rollers 327, a wire 328 wound spirally around the rollers 327 with a predetermined pitch between each winding, and supply pipes 329 through which slurry containing abrasive grains is supplied to the wire 328. As shown in FIG. 8, the wire 328 is drawn in either a single direction or two directions while the slurry, which includes abrasive grains, is supplied to the wire 328. In this state, the wire 328 is pressed against the ingot 13. This enables the wire saw 326 to slice the ingot 13 and produce a plurality of wafers 13a simultaneously.
The silicon monocrystals, in the form of ingots, have an accurate lattice structure. Such monocrystals have certain crystal planes and crystal orientations. The physical and chemical characteristics of the ingot are affected by the crystal orientation of the monocrystals. The crystal orientation refers to a direction perpendicular to the crystal plane. Prior to the slicing, the crystal orientation of the ingot with respect to the axis of the ingot differs from one ingot to another. Accordingly, slicing ingots having different crystal orientations in the same manner results in the wafers having differing characteristics since the relationship between the sliced surface and the crystal plane is not constant in each wafer.
To cope with this problem, an ingot angle setting device is arranged on the wire saw. The support plate holding the ingot is secured to the angle setting device by bolts. In this state, the displacement of the ingot's crystal orientation with respect to the ingot's axis in horizontal and vertical directions is measured by a goniometer. The angle setting device then appropriately aligns the ingot's crystal orientation with the wire traveling direction. More specifically, the angle setting device pivots the ingot along a horizontal plane and along a vertical plane so as to align the crystal orientation of the ingot with a vertical plane perpendicular to each winding of the wire. In other words, as shown in the flowchart of FIG. 50, in the slicing step of the prior art, the ingot, to which the support plate is adhered, is first mounted on the wire saw. The crystal orientation of the ingot is then measured. Afterwards, the ingot is sliced apart into wafers.
However, it is required that each wire saw be provided with an angle setting device. Thus, when using a plurality of wire saws, the cost of the entire system including the wire saws is increased. Furthermore, the attachment of the ingots to the angle setting device is performed manually. This is burdensome for the operator and takes a great deal of time. As a result, attaching the ingots decreases the operational time of the wire saws.
A typical wafer production system includes an adhering step in which the above plates are adhered to the ingot, a mounting step in which the ingots are mounted on the wire saws, an adjusting step in which the crystal orientation of the ingots is measured and adjusted, and a slicing step in which the ingots are sliced. The wafer production system may further include a separating step in which the sliced wafers are separated from one another, a washing step in which the wafers are washed, an inspecting step in which the wafers are inspected, and other steps. In prior art production systems, these steps are performed in an off-line manner. Thus, the mounting, removing, and transporting of the ingots and wafers with respect to the associated apparatus is often performed manually.
However, there is a recent trend in production systems in which the dimensions (diameter and length) of the ingots are becoming larger. This has resulted in the manual mounting, removing, and transporting of the ingots and wafers becoming more burdensome. In addition, since the management of each step is performed manually, it is difficult to increase the manufacturing efficiency of the wafers while upgrading the quality of the wafers.